Synopsis

In contrast to IS, which maps from integers to single integers, the range of a PetscSection is in the space of
contiguous sets of integers. These ranges are frequently interpreted as domains of other array-like objects,
especially other PetscSections, Vecs, and ISs. The domain is set with PetscSectionSetChart() and does not need to
start at 0. For each point in the domain of a PetscSection, the output set is represented through an offset and a
count, which are set using PetscSectionSetOffset() and PetscSectionSetDof() respectively. Lookup is typically using
accessors or routines like VecGetValuesSection().